Re: [ANNOUNCE] Xen 4.15 - release status, branching tomorrow

[Ian Jackson <iwj@xxxxxxxxxxxxxx>]

Jan Beulich writes ("Re: [ANNOUNCE] Xen 4.15 - release status, branching 
tomorrow"):
> On 23.03.2021 17:53, Ian Jackson wrote:
> >> One option of course is, like was just done for 4.13.3, to revert.
> >> Iirc Andrew had some thoughts towards making the new piece of code
> >> conditional upon the original issue actually hitting.
> > 
> > I would be very happy to consider a revert it someone would give me
> > references and explain to me the implications in words of one
> > syllable.
> 
> Reference: e1de4c196a2e "x86/timer: Fix boot on Intel systems using
> ITSSPRC static PIT clock gating"
> 
> Reverting would unbreak Xen on the Ryzen 1800X system where the
> breakage was reported for, and likely a few others. It would at the
> same time re-introduce Xen failing to boot on at least some Icelake
> (and yet newer) systems.

Thanks.  That explanation and the reference makes everything clear for
me.

> >> Another
> >> (somewhat similar) option might be to hide the new piece of code
> >> behind a default-off command line option.
> > 
> > Likewise.
> 
> Well, not sure what to say here. Introducing a command line option
> to allow making Icelake systems boot (by use of the option) while
> keeping things working by default on older hardware is about as
> simple as an explanation here can get, I guess.

Right.

The revert seems unattractive.  Your suggested command line option
sounds like a good workaround to me.  Under the circumstances it seems
like it should default to the old behaviour, as I think you are
suggesting.

So I am be inclined to ask if you, Jan, would prepare a patch
implementing such an option.  Anyone else have any opinions ?

Thanks,
Ian.